Control Systems Engineering

Robust Control of Propane Pre-Cooled Mixed Refrigerant Process for Natural Gas Liquefaction

by Muhammad Shariq Khan

This paper appears in:
Control Automation and Systems (ICCAS), 2010 International Conference on
Date of Conference: 27-30 Oct. 2010
Author(s): Khan, M.S.
Sch. of Chem. Eng. & Technol., Yeungnam Univ., Gyeongsan, South Korea
Mun Kyu Yoon ;  Husnil, Y.A. ;  Moonyong Lee
On Page(s): 702 - 706
Product Type: Conference Publications

Natural Gas are often found at remote locations to bring it to the world market liquefaction is required. In... more Natural Gas are often found at remote locations to bring it to the world market liquefaction is required. In liquefaction natural gas is cooled to around -160°C, hence required considerable amount of energy. To maximize the profit from the existing design it is necessary that the process should operate efficiently, reliably and safely. Hence a good and Robust control is required. Due to tight control strategy the stability is an issue in the main cryogenic heat exchanger(MCHE) and in the Refrigerant flash drum. In this study the C3MR process was considered and the dynamic model was made in Hysys simulator and used to implement the proposed control algorithm. By judiciously choosing control variables we have proposed more robust control strategy and its performance was observed under simulation environment which provide satisfactory robustness for stability and performance.

A Wide Input-Output Voltage Range AC-DC Converter with a Fuzzy PI+D Controller

by Farhad Ghadaki

"Co-authored with Mohammad Bagher Akbari Haghighat", "Co-authored with Mohammad-Ali Shamsi-Nejad"

This paper presents a two stage wide input-output voltage range ac-dc converter. First stage of the converter is a... more This paper presents a two stage wide input-output voltage range ac-dc converter. First stage of the converter is a commercially available front-end boost power factor corrector (PFC) and second stage is a simple step-down dc-dc converter. This work is based on classical off-line ac-dc power supplies architecture. The main improvement is the employment of Fuzzy Proportional-Integral-Derivative (FPI+D) controller to control the step-down converter. The main goal of the utilized controller is to regulate the output voltage in a wide range of reference voltage and load changes. Achieving these goals is possible by applying this robust controller that can handle inherent nonlinearities of dc-dc converters operating in both continuous-conduction-mode (CCM) and discontinuous-conduction-mode (DCM). Besides simulation results, a 200W universal-line hardware prototype was built to evaluate the proposed scheme experimentally. Developed prototype has the input voltage range of 85-265 Vac and the wide output voltage range between 10-200 Vdc.

CONTROL OF DYNAMIC RESPONSE OF A COMPLIANT OFFSHORE STRUCTURE

by Syed Khaleeq Ahmad

Sliding mode Control of piezoelectric valve regulated pneumatic actuator for MRI-compatible robotic intervention

by Gregory Fischer

Control of an Inverted Pendulum Using an Ionic Polymer-Metal Composite Actuator

by Maarja Kruusmaa

A. Hunt, Z. Chen, X. Tan, M. Kruusmaa. Control of an Inverted Pendulum Using an Ionic Polymer-Metal Composite Actuator, In Proc. of 2010 IEEE/ASME International Conference on Advanced Intelligent Mechatronics.

Ionic polymer-metal composites (IPMCs) are electroactive materials that bend under an applied electric field. Existing... more Ionic polymer-metal composites (IPMCs) are electroactive materials that bend under an applied electric field. Existing work has typically dealt with the control of IPMC actuators themselves. In this paper we investigate the stabilization of an inverted pendulum on a cart using an IPMC actuator. Different from the traditional setting of cart- pendulum systems, we require that the voltage on the IPMC actuator stay close to zero, to prolong the actuator life and reduce power consumption. A state-space model is developed for the system, based on which an LQR controller together with an observer is designed. The proposed control scheme is able to stabilize the inverted pendulum for the entire duration of the experiment (five minutes). These results indicate that IPMC actuators hold potential for more sophisticated control applications.

Using SysML in Systems Design

by Alberto Sampaio

ICIII '09

System of systems involves several secondary systems working together with its creation gathering the knowledge of... more System of systems involves several secondary systems working together with its creation gathering the knowledge of several distinct disciplines and teams, each one with their own background and methods, leading to a difficult communication between them. SysML, a language originated from UML, enables that communication, without background interference, with the use of a rich notation for systems design. This paper analyzes its use through the experience gained in the design of a chemical system with SysML.

Direct control based on sliding mode techniques for multicell serial chopper

by Leonardo Amet

Using Genetic Algorithms to Design a Fuzzy Logic Controller for a pH Reactor: An Object Approach

by Gustavo Sanchez

PhD Thesis - Virtual Metrology for Plasma Etch Processes

by Shane Lynn

PhD Thesis. Examined March 2011.

Plasma processes can present difficult control challenges due to time-varying dynamics and a lack of relevant and/or... more Plasma processes can present difficult control challenges due to time-varying dynamics and a lack of relevant and/or regular measurements. Virtual metrology (VM) is the use of mathematical models with accessible measurements from an operating process to estimate variables of interest. This thesis addresses the challenge of virtual metrology for plasma processes, with a particular focus on semiconductor plasma etch. Introductory material covering the essentials of plasma physics, plasma etching, plasma measurement techniques, and black-box modelling techniques is first presented for readers not familiar with these subjects. A comprehensive literature review is then completed to detail the state of the art in modelling and VM research for plasma etch processes.

To demonstrate the versatility of VM, a temperature monitoring system utilising a state-space model and Luenberger observer is designed for the variable specific impulse magnetoplasma rocket (VASIMR) engine, a plasma-based space propulsion system. The temperature monitoring system uses optical emission spectroscopy (OES) measurements from the VASIMR engine plasma to correct temperature estimates in the presence of
modelling error and inaccurate initial conditions. Temperature estimates within 2% of the real values are achieved using this scheme.

An extensive examination of the implementation of a wafer-to-wafer VM scheme to estimate plasma etch rate for an industrial plasma etch process is presented. The VM models estimate etch rate using measurements from the processing tool and a plasma impedance monitor (PIM). A selection of modelling techniques are considered for VM modelling, and Gaussian process regression (GPR) is applied for the first time for VM
of plasma etch rate. Models with global and local scope are compared, and modelling schemes that attempt to cater for the etch process dynamics are proposed. GPR-based windowed models produce the most accurate estimates, achieving mean absolute percentage errors (MAPEs) of approximately 1.15%. The consistency of the results presented suggests that this level of accuracy represents the best accuracy achievable for
the plasma etch system at the current frequency of metrology.

Finally, a real-time VM and model predictive control (MPC) scheme for control of plasma electron density in an industrial etch chamber is designed and tested. The VM scheme uses PIM measurements to estimate electron density in real time. A predictive functional control (PFC) scheme is implemented to cater for a time delay in the VM system. The controller achieves time constants of less than one second, no overshoot, and excellent disturbance rejection properties. The PFC scheme is further expanded by adapting the internal model in the controller in real time in response to changes in the process operating point.

Real-Time Virtual Metrology and Control of Plasma Electron Density in an Industrial Plasma Etch Chamber

by Shane Lynn

18th IFAC World Congress, Aug. 2011.
co-Authored with Niall MacGearailt and John V. Ringwood

Plasma etching is a semiconductor manufacturing process during which material is removed from the surface of silicon... more Plasma etching is a semiconductor manufacturing process during which material is removed from the surface of silicon wafers using gases in plasma form. A host of chemical and
electrical complexities make the etch process notoriously difficult to model and troublesome to control. This work demonstrates the use of a real-time model predictive control scheme to maintain a consistent plasma electron density in the presence of disturbances to the ground path of the chamber. The electron density is estimated in real time using a virtual metrology model based on plasma impedance measurements. Recursive least squares is used to update the controller model parameters in real time to achieve satisfactory control of electron density over a wide operating space.

Estimation and Control in Semiconductor Etch: Practice and Possibilities

by Shane Lynn

IEEE Transactions in Semiconductor Manufacturing. Vol. 23, No. 1, Feb 2010.

Semiconductor wafer etching is, to a large extent, an open-loop process with little direct feedback control. Most... more Semiconductor wafer etching is, to a large extent, an open-loop process with little direct feedback control. Most silicon chip manufacturers rely on the rigorous adherence to a “recipe” for the various etch processes, which have been built up based on considerable historical experience. However, residue buildup and difficulties in achieving consistent preventative maintenance operations lead to drifts and step changes in process characteristics. This paper examines the particular technical difficulties encountered in achieving consistency in the etching of semiconductor wafers and documents the range of estimation and control techniques currently available to address these difficulties. An important feature of such an assessment is the range of measurement options available if closed-loop control is to be achieved.

Modeling And Simulation Of Prolate Dual-Spin Satellite Dynamics In An Inclined Elliptical Orbit: Case Study Of Palapa B2R Satellite

by Agus Budiyono

Symposium on Aerospace Science and Technology, Jakarta, 2005

In response to the interest to re-use Palapa B2R satellite nearing its End of Life (EOL) time, an idea to incline the... more In response to the interest to re-use Palapa B2R satellite nearing its End of Life (EOL) time, an idea to incline the satellite orbit in order to cover a new region has emerged in the recent years. As a prolate dual-spin vehicle, Palapa B2R has to be stabilized against its internal energy dissipation effect. This work is focused on analyzing the dynamics of the reusable satellite in its inclined orbit. The study discusses in particular the stability of the prolate dual-spin satellite under the effect of perturbed field of gravitation due to the inclination of its elliptical orbit. Palapa B2R physical data was substituted into the dual-spin's equation of motion. The coefficient of zonal harmonics J2 was induced into the gravity-gradient moment term that affects the satellite attitude. The satellite's motion and attitude were then simulated in the perturbed gravitational field by J2, with the variation of orbit's eccentricity and inclination. The analysis of the satellite dynamics and its stability was conducted for designing a control system for the vehicle in its new inclined orbit.

Onboard Multivariable Controller Design for a Small Scale Helicopter Using Coefficient Diagram Method

by Agus Budiyono

Proceedings of the ICEST, Seoul, Korea, May 2005

A mini scale helicopter exhibits not only increased sensitivity to control inputs and disturbances, but also higher... more A mini scale helicopter exhibits not only increased sensitivity to control inputs and disturbances, but also higher bandwidth of its dynamics. These properties make model helicopters, as a flying robot, more difficult to control. The dynamics model accuracy will determine the performance of the designed controller. It is attractive in this regards to have a controller that can accommodate the unmodeled dynamics or parameter changes and perform well in such situations. Coefficient Diagram Method (CDM) is chosen as the candidate to synthesize such a controller due to its simplicity and convenience in demonstrating integrated performance measures including equivalent time constant, stability indices and robustness. In this study, CDM is implemented for a design of multivariable controller for a small scale helicopter during hover and cruise flight. In the synthesis of MIMO CDM, good design common sense based on hands-on experience is necessary. The low level controller algorithm is designed as part of hybrid supervisory control architecture to be implemented on an onboard computer system. Its feasibility and performance are evaluated based on its robustness, desired time domain system responses and compliance to hard-real time requirements.

The JET PCU project: an international plasma control project

by Gianmaria De Tommasi

published in 'Fusion Engineering and Design', 2008

This paper describes the new JET enhancement project “Plasma Control Upgrade” (PCU). Initially aimed at an overhaul of... more This paper describes the new JET enhancement project “Plasma Control Upgrade” (PCU). Initially aimed at an overhaul of JET plasma control capabilities it was eventually focused on improving the vertical stabilisation (VS) system ability to recover from large ELM (edge localised mode) perturbations. The paper describes the results of the first two years where the activity was aimed principally at researching a solution that could be implemented within the timing and budget constraints. A very important task was that of improving the modelling of JET plasma, iron core and passive structures. Using dedicated experiments, the models were progressively refined until it was possible not just to explain the experimental data but predict the VS system behaviour.

At the same time the project team studied the best options for power supply (PS) and control system upgrades and evaluated whether a change of turns in the stabilisation coil was desirable and possible.

A new fast radial field power supply is now being ordered and the VS control system is being upgraded.

Plasma strike-point sweeping on JET tokamak with the eXtreme Shape Controller

by Gianmaria De Tommasi

published in 'IEEE Transactions on Plasma Science', 2008

The high-energy ionized particles collected by the divertor structures in a tokamak reactor cause a localized thermal... more The high-energy ionized particles collected by the divertor structures in a tokamak reactor cause a localized thermal load around the strike-points, which are the intersections of the separatrix with the divertor tiles. To spread on a larger region this thermal load, it is convenient to resort to a sweeping, i.e., a periodical movement of the strike-points. This paper introduces the new model-based sweeping algorithm recently implemented on the Joint European Torus tokamak, within the eXtreme Shape Controller architecture.

Design, implementation and test of the XSC extreme shape controller in JET

by Gianmaria De Tommasi

published in 'Fusion Engineering and Design', 2005

A new model-based plasma current and shape controller has been set up and tested on the JET Tokamak with the existing... more A new model-based plasma current and shape controller has been set up and tested on the JET Tokamak with the existing active circuits and control. The installation has been carried out without causing any interference to the plasma operation and without requiring a long commissioning time. Eventually, the new controller was used on really extremely shaped internal transport barrier experiments at high poloidal beta and in the presence of quite large variations of the plasma current density profile (variation range Δβpol up to 1.5 and Δli up to 0.5). The extreme shape controller (XSC) controller architecture and philosophy also offer new interesting opportunities, e.g., the separatrix sweeping on the divertor plates without significantly affecting the overall plasma shape, and the possibility of improving the overall tokamak performance via combined control of plasma shape, current and profile. The adopted methodology constitutes also an important test bed for feedback control strategies of ITER relevance.

The system architecture of the new JET shape controller

by Gianmaria De Tommasi

published in 'Fusion Engineering and Design', 2005

This paper describes the installation of the new JET Shape Controller System [M. Garribba, R. Litunovsky, P. Noll, S.... more This paper describes the installation of the new JET Shape Controller System [M. Garribba, R. Litunovsky, P. Noll, S. Puppin, The new control scheme for the JET plasma position and current control system, in: Proceedings of the 15th SOFE Conference, Massachusetts, 1993, pp. 33–36; F. Sartori, A. Cenedese, Plasma position and current control management at JET, in: Proceedings of the 42nd IEEE Conference on Decision and Control, Maui, 2003] especially focusing on the addition of the Extreme Shape Controller [G. Ambrosino, et al., A new shape controller for extremely shaped plasmas in JET, Fusion Eng. Des. 66–68 (2003) 797–802]. The activity was performed by the JET Operator in co-operation with the ENEA-CREATE design team, and involved both changes in the hardware and system software of JET and tuning of the proposed Extreme Shape Controller (XSC) design to satisfy the practical requirements of tokamak operation. The application of 10 years experience of controller implementation and commissioning combined with a modern and efficient modelling and design methodology has allowed an unprecedented fast and easy commissioning of the new system.

The Software Architecture of the New Vertical Stabilization System for the JET tokamak

by Gianmaria De Tommasi

published in 'IEEE Transactions on Plasma Science', 2010

The need to improve the performance of modern tokamak operations has led to a further development of the plasma shape... more The need to improve the performance of modern tokamak operations has led to a further development of the plasma shape and position control systems. In particular, extremely elongated plasmas, with high vertical-instability growth rate, are envisaged to reach the required performance for ignition. This request for better performance from the experimentalists' side has motivated the development of the new vertical-stabilization (VS) system at the JET tokamak, which has been proposed within the Plasma Control Upgrade project. The main aim of the project is to enhance the capabilities of the plasma vertical position control system in order to operate with very highly elongated plasmas in the presence of large perturbations. This paper focuses on the new software architecture of the VS system, which relies on a highly configurable real-time framework. Due to its flexibility, the new VS system executes different control algorithms, and it schedules the one which maximizes the performance in each plasma phase.

The Joint European Torus - Plasma position and shape control in the world's largest tokamak

by Gianmaria De Tommasi

published in 'IEEE Control Systems Magazine', 2006

This paper describes some of the control problems faced by the engineers working at the Joint European Torus (JET),... more This paper describes some of the control problems faced by the engineers working at the Joint European Torus (JET), focusing mostly on the control of plasma shape, position, and current. It details the control methodology used on JET, which can serve as guide for the design of sophisticated multivariable, yet user friendly, controllers for the next generation of fusion experiments.

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